Fluid discharge casing



y 1969 G. w. SCHEPER, JR 3,452,782

' FLUID DISCHARGE CASING Filed July 8, 1965 FIG. I

(PRIOR ART) FIQZ INVENTOR: GEORGE W- SCHEP ERJR.

ms ATTORNEY-T;

United States Patent 3,452,782 FLUID DISCHARGE CASING George W. Scheper,Jr., Schenectady, N.Y., assignor to General Electric Company, acorporation of New York Filed July 8, 1966, Ser. No. 563,812 Int. Cl.F16d 1/00, 1/12 US. Cl. 138-37 6 Claims ABSTRACT OF THE DISCLOSURE Thepresent invention relates to casings for the flow of gases or vapors.More particularly, it relates to casings for the passage of Workingfluid from a large heat engine such as a gas turbine.

It is common in the gas turbine art to let out exhaust gases orcompressor discharge air in a regenerative cycle at locations spacedradially as well as axially from the working members of the machine. Dueto limitations of space, etc., it is not always practical to have theair discharge and the gas exhaust casings perfectly coaxial with theturbine. Thus, it is common to use an exhaust or discharge system orturning hood to conduct the fluid therein to a more remote location.

For purposes of description, the present invention will be described asit applies to a gas turbine exhaust casing, but it should be understoodthat the same principles and the same invention will apply as well tothe compressor discharge casing. The exhaust turning hood is thatconduit which receives the turbine exhaust gases and changes theirdirection of flow. The turning hood includes the axial turbine dischargeannular diffusing passage and the duct into which the annular diffusingpassage discharges. With such a turning hood, there is within a gasturbine exhaust annulus, an inherent pressure variation in the bucketexit plane and parallel planes immediately downstream of the last stageturbine buckets. That is, within the discharge annulus, there is lowergas pressure on that side of the annulus toward the direction to whichthe turning hood directs the gases and a higher gas pressure in thatpart of the annulus away from the direction of turning. This pressuredifferential produces a bucket vibration stimulus, one per revolution,in the turbine rotor, which could be undesirable depending on itsamplitude. The present invention is useful in substantiallyreducing theamplitude of this stimulus.

Accordingly, it is an object of the present invention to provide a gasturbine compressor discharge or turbine exhaust casing with improveduniformity of fluid pressure within its annular passage.

Another object is to provide a gas turbine having compressor dischargeand exhaust casings which substantially reduce the blade or bucketvibration, causing stimulus inherent in prior art casings.

Other objects, advantages and features of the present invention willbecome apparent from the following description of one example thereof,when taken in connection with the accommpanying drawing.

Brieflly stated, the present invention is practiced in one form by a gasturbine exhaust annulus discharging into a turning hood. At intermediatepoints between the inlet and the end of the exhaust diffusing annulusare circumferential slots through the outer wall thereof. The

circumferential slots each communicate with an annular manifold situatedradially outside of the exhaust annulus. This provides an additionalcommunication path between opposite sides of the exhaust annulus. Theresulting boundary layer removal in the higher pressure region and addedflow therein causes correspondingly decreased flow in the lower pressureregion for the purpose of improved uniformity of pressure therein.

Referring now to the drawing:

FIG. 1 is a longitudinal elevation of a gas turbine exhaust systemtypical of the prior art.

FIG. 2 is a longitudinal elevation of a gas turbine exhaust systemaccording to the present invention.

In FIG. 1, a turbine rotor 2 is partially shown, carrying its last stagerotor buckets 4 thereon. Rotor buckets 4 project radially into path 6 ofthe turbine working fluid, which path communicates with and dischargesinto annular diffusing exhaust passage 8. Exhaust passage 8 is coaxialwith turbine rotor 2 and typically comprises a cylindrical or conicalinner wall or shell 10 and a conical outer wall or shell 12. The flowarea increases in the direction of flow to provide a diffusing passagewhich produces a substantial pressure rise, thereby recovering some ofthe kinetic energy leaving buckets 4.

At its outer extremity, annular exhaust passage 8 discharges intoexhaust duct 14, which may extend in any direction necessitated by spacerequirements, thus effecting the turn from axial flow. Exhaust duct 14is defined by duct casing 22. Inner and outer shells 10 and 12, andexhaust duct 14 comprises a turning hood. In this exhaust arrangement,typical of the prior art, there is a pressure differential within theannular exhaust passage 8 immediately downstream of the last stage rotorbuckets 4 such that, in the area designated as L, the gas dischargepressure is lower than at the opposite side of the annulus in the areadesignated H. This is the pressure differential of the prior art towhich the present invention is directed.

Referring now to FIG. 2, wherein like numbers refer to like elements inFIG. 1, the conical outer shell 120 of the annular exhaust passage ismodified as compared to the shell 12 shown in FIG. 1, by providing, atspaced axial positions, annular circumferential slots or apertures 16through the conical outer shell 120. Annular exhaust passage 80communicates by way of slots 16 with annular manifolds 18 which surroundthe conical outer shell and are defined by partitions 20. Slots 16 mayor may not totally surround the outer shell 120. Manifolds 18 might alsobe positioned radially inward of passage 80. There are as many annularmanifolds 18 as there are slots 16, and manifolds 18 do not directlycommunicate with each other. The undescribed remainder of the structureof FIG. 2 is the same as that described in FIG. 1.

The operation of the present invention will best be understood byreference again to FIG. 1 as a starting point. In steady state operationof the turbine represented in FIG. 1, there will be a lower gas pressurein the area designated L than that in the area designated H withinannular exhaust passage 8, this being the unmodified exhaust passage ofthe prior art. This pressure differential persists as an inherentpressure variation during operation of the turbine, and is inherent inall types of turning hoods due to the change in direction of fluid flow.Now, imposing this condition as a reference point on the exhaust systemshown in FIG. 2, the operation is as follows:

Higher pressure discharge gas from that part of the exhaust annulus 80in the region designated H, flows through slots 16 into annularmanifolds 18. The gas flows inside the manifolds 18 around to the otherside of the manifolds near the low pressure region L The flow leavesmanifolds 18, reentering annular duct 80 due to the lower pressuretherein. This flow, through slots 16 and annular manifolds 18, is ofcourse a small proportion of the total gas flow, the bulk of itcontinuing straight through annular exhaust duct 80 and turning intoexhaust duct 14. The slots 16 and manifolds 18 create a secondary flowfrom the high pressure region to the low pressure region, therebyimproving the diffuser action in the high pressure region due to removalor suction of the low momentum fluid of the boundary layer. In addition,due to the fact that there is entry of gas flow from mani folds 18through slots 16 in the low pressure, L region, thus interfering withdirect exhaust flow in that region and diminishing the diffuser actionthere, the direct exhaust flow in the low pressure region is slightlyreduced. Thus, with exhaust flow in the H high pressure region slightlyincreased and exhaust flow in the L low pressure region slightlydecreased, the tendency to equalization of flow is also a tendencytoward equalization of pressure. In practice, it has been found that thepressure variation, or differential between H and L regions, resultingfrom the use of the present invention is on the order of A to /2' of thepressure variation between the H and L regions of an unmodified exhaustsystem, as in FIG. 1. To that extent, then, the undesirable effect ofthe bucket vibration stimulus, occuring at a fundamental frequency ofonce per revolution, is decreased or modified by a factor of A to /2 Itwill be apparent that the above-described invention has necessarily beendescribed in one environment, that being in an exhaust turning hood. Thepresent invention is equally applicable to other environments such as,for example, compressor discharge turning hoods, where the same pressuredifferential phenomenon occurs. Furthermore, the number of slots 16 andannular manifolds 18 is variable according to the size of the machine,the configuration of the hood, etc.

It may occur to others of ordinary skill in the art to makemodifications of the present invention which will lie within the conceptand scope thereof. Accordingly, it is intended that the invention benot. limited by the details by which it has been described but that itencompass all within the purview of the following claims.

What is claimed is:

1. A fluid turning hood comprising:

an inner shell and an outer shell substantially defining an open-endedannular diffusing flow passage therebetween,

a casing defining a duct in communication with said annular passage atone end thereof,

said duct angularly disposed relative to said annular passage, and

conduit means external to said annular passage providing communicationbetween diametrically opposed portion thereof.

2. A fluid turning hood according to claim 1 in which 4 said conduitmeans comprises an annular manifold disposed circumferentially aroundsaid outer shell, said outer shell defining an aperture effectingcommunication between said manifold and said annular passage, saidaperture being the sole opening of said manifold.

3. A fluid turning hood according to claim 2 further including aplurality of said annular manifolds and said apertures, said manifoldsin separate and sole communication through said apertures with saidannular flow passage.

4. A fluid turning hood according to claim 2 in which said aperture iscontinuous, extending circumferentially between said annular passage andsaid manifold.

5. An annular passage adapted to be disposed in communication at one ofits ends with an annular workingfluid path of a turbomachine,

said annular passage surrounded by a manifold,

a circumferential aperture in the outer wall of said annular passageeffecting communication between said passage and said manifold,

said annular passage communicating at its other end with a duct defininga flow passage disposed at an angle relative to the axis of said annularpassage.

6. A turning hood for fluids in which annular fluid flow made to changeits direction sustains a pressure differential in correspondinglocations around the annulus, fluid pressure within the first sideportion of the annulus toward the turn being generally lower than fluidpressure within the second side portion of the annulus away from thedirection of turn, comprising:

an inner shell and an open-ended outer shell substantially defining saidannulus therebetween,

an annular manifold disposed circumferentially relative to said annulus,and

means between said manifold and said annulus to effect communicationbetween said manifold and said annulus on at least the first and secondside portions thereof.

References Cited UNITED STATES PATENTS 2,666,453 1/ 1954 Davidson 138372,781,057 2/ 1957 Fletcher 138-39 2,948,148 8/ 1960 Anfreville.

FOREIGN PATENTS 94,591 1/ 1963 Denmark.

SAMUEL ROTHBERG, Primary Examiner.

US. Cl. X.R. 253-39

